1. Field of the Invention
This invention relates to an improvement of thermal head used in thermal recording, and more particularly, to a composition of an electrically energized resistive film.
2. Description of the Prior Art
Heretofore, such a thermal head in the prior art, for instance as shown in FIG. 1, comprises a substrate 1 made of electrically insulative material such as alumina, a resistive film 2 made of tantalum nitride (Ta.sub.2 N), and an electrode 3 made of gold (Au), aluminum (Al), copper (Cu) or other metal, which are sequentially laminated, wherein a certain voltage is applied to the resistive film 2 through the electrode 3 to generate Joule heat in the film 2 to function as thermal head. A protective film 21 is formed on the electrode 3.
In this conventional thermal head, since the affinity between Ta.sub.2 N, the material of resistive film 2, and Au, Al or Cu, the material of electrode 3, is poor, the junction strength of the resistive film 2 and the electrode 3 is extremely weak, and the electrode 3 may be easily separated from the resistive film 2 when an external force is applied in operation, so that predetermined voltage may not be applied to the resistive film 2. Accordingly, in this thermal head, the resisitive film 2 cannot be heated to a desired temperature by Joule heat, and the function as thermal head may not be achieved or printing defect may be caused.
In order to prevent such electrode separation in the thermal head in the prior art a thermal head having an adhesion layer 4 possessing an intensified affinity for both the resistive film 2 and the electrode 3 interposed between them was proposed as shown in FIG. 2. However, in this thermal head, although the separation of electrode 3 may be effectively prevented by the interposition of the adhesion layer 4, this layer must be separately formed between the film 2 and electrode 3, which makes the manufacturing process of thermal head more complicated, and impairs the productivity and yield, thereby increasing the cost of thermal head as a product.